The particle counter apparatus is particularly intended for use in counting particles in a fluid flowing in a pipe or a pipeline located in areas with difficult access such as for example on an ocean or sea bed. This may involve hydrocarbons flowing preferably in a pipe or a pipeline which may form a part of subsea production equipment or a pipeline for transport of hydrocarbons from the production equipment to land or interim storage in an installation at or below the surface. The invention may also be employed in areas where there is a risk of explosion and/or fire.
When the number of particles present in a fluid has to be counted, the particles should be as uniformly distributed in the fluid as possible. Should the particles for some reason or other have a tendency to agglomerate in the fluid, it could give an entirely false picture of the particle density in the fluid if the fluid sample removed for counting particles either contains fluid with a particle density which is below or above the real particle density in the fluid. It is therefore advantageous to mix the fluid in order to obtain a uniform distribution of particles in the fluid before a fluid sample is removed for counting particles in the fluid.
From the prior art it is known from EP 75977 A2 to install a static mixer in a mixing zone in a pipeline for mixing a fluid flowing in the pipeline. The mixing zone is provided some distance upstream of the outlet for fluid samples and comprises slanting blades on the inside of the pipeline which cause the fluid to acquire a rotating motion. According to the description, the intake for the fluid sample must not be placed in the wake of the mixer. The intake must therefore be understood to be located a good distance downstream of the mixer. A similar static mixer is also disclosed in EP 41825 A1, which is made for use in unloading systems for unloading oil from a vessel. Samples are taken in order to check the quality of the oil. None of these systems are arranged so that there is a pressure drop in the pipeline between drawing fluid from and return of fluid to the pipe flow. The fluid samples therefore have to be pump-driven.
Another method of mixing fluids is disclosed, for example, in GB 2 357 710 A, GB 2 164 021 A and U.S. Pat. No. 4,307,620, where the fluid sample removed for analysis is injected into the pipe flow upstream of the outlet for the fluid sample. The injection of the fluid sample should then cause the fluid in the pipe flow to be mixed. This requires continuous injection of fluid into the pipe flow, and possibly an accurately controlled injection of a sample in relation to tapping a new sample. All these devices require a pump in order to pump the fluid which has to be injected into the pipe flow.
A further method of mixing fluid is disclosed in GB 2 425 971 A, where a portion of a pipe or a pipeline is equipped with one or more bends in order to mix the fluid.
In WO 2004/057306 A1, which is the applicant's own patent application, a particle counter is disclosed for counting particles in a fluid sample removed from a fluid pipe flow. This application, however, relates to the particle counter as such and no mention is made of how electric power can be provided when the particle counter has to be used for investigation of fluid pipe flows in pipes or pipelines in areas with difficult access, such as for example pipes and pipelines located in deep water or in areas where there is a risk of fire and/or explosion. Nor is there any mention of how to obtain a mixing of the pipe flow, thereby causing any particles in the pipe flow to be uniformly distributed before a fluid sample is removed for analysis.
Since the present particle counter apparatus is intended for use in an environment which is difficult of access or in surroundings where there is a risk of fire and/or explosion, it is also an advantage for the particle counter to be entirely or to the greatest possible extent self-sufficient in the energy required. This avoids the use of cables for supplying electric energy for operating the particle counter. Electric cables will constitute a safety risk in areas where there is a risk of fire and/or explosion and in deep water it is a disadvantage to have to lay cables from the surface to equipment located below the surface. In other ways too it is an advantage if the whole particle counter apparatus can function as far as possible without external intervention or supply of electric power or other energy. This applies, for example, to the light source for particle counting and image recognition, data processing, cable-free communication for transmitting data from the particle counter and/or control signals for controlling the particle counter and other parts of the particle counter apparatus.